AMSTERDAM — Joint distraction via temporary external fixation may provide a powerful new tool in the management of severe knee osteoarthritis in younger patients, Dr. Floris P.J.G. Lafeber said at the annual European Congress of Rheumatology.
The purpose is not to provide an alternative to joint replacement surgery, but rather to delay the procedure until a point in life where the first prosthesis is likely to be the only one the patient will ever need, explained Dr. Lafeber of Utrecht University Medical Center, the Netherlands.
Patients with knee osteoarthritis (OA) secondary to athletic trauma often develop end-stage disease before age 55. Give a 55-year-old a prosthetic joint, however, and the patient is likely to require a complex revision by age 70. It's an expensive, challenging procedure, and the clinical results are not as good as the first time around, Dr. Lafeber said at the congress.
Joint distraction provides the ravaged knee with an extended restorative vacation. This is accomplished by placing pins in both bony ends of the knee joint, then joining the pins together in an external fixation frame that maintains 5 mm of joint distraction by x-ray.
The separation eliminates mechanical stresses on the articular surfaces, preventing further cartilage wear and tear. In addition, the lessened load on bone is believed to result in temporary osteopenia within the distraction area, he noted. This softened, demineralized bone also reduces stress on the cartilage. And when the fixation frame is removed, the bone reloading triggers increased bone turnover with release of growth factors thought important to cartilage repair.
Thin flexible wires or springs in the distraction frame promote intermittent intraarticular fluid pressure changes. This is thought to be necessary for adequate nutrition of chondrocytes during the distraction period, which lasts 2–3 months. That's about as long as patients are willing to put up with the inconvenience, he said.
The first joint distraction studies were published over 12 years ago by Italian investigators working with hip OA patients. More recent work by Dr. Lafeber and his fellow investigators and several others has involved posttraumatic severe ankle OA in joint fusion candidates. Significant improvements in pain and function in three-quarters of patients have been documented with follow-up of 2–16 years.
To date, the pioneering work on knee OA by Dr. Lafeber's group involves seven patients with a maximum follow-up of 2 years. He termed the results “very promising.” Pain scores averaging 8 on a scale of 10 at baseline dropped to 1 in the first 6 months, with the benefit sustained during the remainder of follow-up. Joint function improved from 20% of the maximum score to 80%.
“The results are seen even faster than in ankle distraction, with a similar degree of clinical benefit,” said Dr. Lafeber.
A key unanswered question is whether these clinical benefits are accompanied by underlying structural changes in cartilage and bone. Dr. Lafeber and coworkers are obtaining serial x-rays and MRIs and gathering serum and urine samples for future analysis of cartilage and bone turnover markers in an effort to resolve the issue. Blinded scoring of joint status by arthroscopic examination shows preliminary evidence of benefit.
“We don't think the results are due to a placebo effect,” he said.
The separation eliminates mechanical stresses on the articular surfaces, preventing further cartilage wear. DR. LAFEBER